1. Field
The present invention relates to articulated arms and coordinate measurement, and more particularly to coordinate measurement machines.
2. Description of the Related Art
Rectilinear measuring systems, also referred to as coordinate measuring machines (CMMs) and articulated arm measuring machines, are used to generate highly accurate geometry information. In general, these instruments capture the structural characteristics of an object for use in quality control, electronic rendering and/or duplication. One example of a conventional apparatus used for coordinate data acquisition is a portable coordinate measuring machine (PCMM), which is a portable device capable of taking highly accurate measurements within a measuring sphere of the device. Such devices often include a probe mounted on an end of an arm that includes a plurality of transfer members connected together by joints. The end of the arm opposite the probe is typically coupled to a moveable base. Typically, the joints are broken down into singular rotational degrees of freedom, each of which is measured using a dedicated rotational transducer.
During a measurement, the probe of the arm is moved manually by an operator to various points in the measurement sphere. At each point, the position of each of the joints must be determined at a given instant in time. Accordingly, each transducer outputs an electrical signal that varies according to the movement of the joint in that degree of freedom. Typically, the probe also generates a signal. These position signals and the probe signal are transferred through the arm to a recorder/analyzer. The position signals are then used to determine the position of the probe within the measurement sphere. See e.g., U.S. Pat. Nos. 5,829,148 and 7,174,651, which are incorporated herein by reference in their entireties. In some instances, the user of a CMM may want to leave the arm in a fixed position for a period of time. One example of a fixed position would the CMM's resting position. In such cases, the arm should remain in its fixed position so that it does not fall and cause damage to the arm or the surface on which it falls. Additionally, the arm should move from its fixed position upon application of a high amount of force or upon an impact upon the arm to avoid damage to the arm from the high amount of force or impact.
Generally, there is a demand for such machines with a high degree of accuracy and stability, high reliability and durability, substantial ease of use and low cost, among other qualities. The disclosure herein provides improvements of at least some of these qualities.